Flexible sensor for measuring flex or torque

ABSTRACT

A flexible sensor that includes a printed circuit board (PCB), a capacitive structure on the PCB, and mechanical coupling sites. The PCB includes a slot extending from an outer edge of the PCB to an inner portion of the PCB, and the slot defines a first edge and a second edge facing the first edge. The first and second edges are separated by a gap when the PCB is in an unflexed state. The slot is configured to permit the PCB to flex so as to vary a relative position of the first edge with respect to the second edge. The capacitive structure on the PCB includes a first edge electrode on a portion of the first edge of the PCB, and a second edge electrode on a portion of a second edge of PCB. The second edge electrode is aligned with the first edge electrode across the slot.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Patent Application No. 62/423,382, entitled “Flexible Sensor,” filedNov. 17, 2016, which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

This disclosure generally relates mechanical sensors, and moreparticularly to mechanical sensors for measuring mechanical flex andtorque in a structural member or mechanical joint.

BACKGROUND

Mechanical sensors are used to measure physical variations in mechanicaldevices and mechanical structures. Mechanical sensors can measureflexure, stress, and torque in mechanical devices and structures. Somesensors convert mechanical displacement into electrical values throughchanges in resistance and capacitance of electrical components in thesensors.

SUMMARY

This disclosure describes flexible sensors for measuring the flex ortorque of mechanical structures or mechanical joints, such as actuablejoints of a robotic device. In addition, this disclosure describessystems and methods for measuring flex or torque in mechanicalstructures or joints using a flexible sensor.

In general, innovative aspects of the subject matter described in thisspecification can be embodied in flexible sensor that includes a printedcircuit board (PCB), a capacitive structure on the PCB, and mechanicalcoupling sites. The PCB includes a slot extending from an outer edge ofthe PCB to an inner portion of the PCB, and the slot defines a firstedge and a second edge facing the first edge. The first and second edgesare separated by a gap when the PCB is in an unflexed state. The slot isconfigured to permit the PCB to flex so as to vary a relative positionof the first edge with respect to the second edge. The capacitivestructure on the PCB includes a first edge electrode on a portion of thefirst edge of the PCB, and a second edge electrode on a portion of asecond edge of PCB. The second edge electrode is aligned with the firstedge electrode across the slot. The mechanical coupling sites arearranged on the PCB such that mechanical variations in a structure towhich the sensor is attached cause the PCB to flex and vary the relativeposition of the first edge electrode with respect to the second edgeelectrode. This and other implementations can each optionally includeone or more of the following features.

In some implementations, the sensor includes a control circuitelectrically connected to the first edge electrode and the second edgeelectrode, where the control circuit configured to apply a drive signalto the capacitive structure.

In some implementations, the sensor includes a control circuitelectrically connected to the capacitive structure and configured tomeasure variations in a capacitance between the first edge electrode andthe second edge electrode.

In some implementations, the control circuit is further configured todetermine an amount of mechanical flex in a structure to which thecoupling sites of the PCB are attached based on the measured variationsin the capacitance of the capacitive structure.

In some implementations, the control circuit is a microprocessor.

In some implementations, the control circuit determines an amount ofmechanical flex in a structure by correlating a measured variation incapacitance of the capacitive structure to a flexure value among a setof stored values in a lookup table.

In some implementations, the coupling sites are arranged on oppositesides of the slot.

In some implementations, the portion of the first edge of the PCB andthe portion of the second edge of the PCB are proximate to the outeredge of the PCB.

In some implementations, a first coupling site is located proximate tothe outer edge of the PCB and a second coupling site is located on asame side of the slot as the first coupling site and spaced from thefirst coupling site along a length of the slot.

Some implementations include a robotic device where the sensor ismounted on a member of the robotic device.

Particular implementations of the subject matter described in thisspecification can be implemented so as to realize one or more of thefollowing advantages. Implementations may provide economicallyinexpensive flex/torque sensors because the sensors may be simply formedfrom inexpensive, widely-available materials. Implementations mayprovide flex/torque sensors that can readily be incorporated intoelectronic printed circuit boards of a self-actuating mechanical devicesuch as a robotic device. Implementations may provide flex torquesensors that do not require metallic housings.

The details of one or more implementations of the subject matter of thisdisclosure are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A shows a top view and a cross-sectional view of an exampleflexible sensor.

FIG. 1B depicts an example operation of the example flexible sensor.

FIG. 1C shows an isometric view of a second example flexible sensor.

FIG. 2 shows a top view, cross-section view, and isometric view of athird example flex sensor.

FIG. 3 is a block diagram of an example system for controlling one ormore flex sensors according to implementations of the presentdisclosure.

FIG. 4 illustrates an example of flexible sensors coupled to amechanical device.

FIG. 5 depicts a schematic diagram of a computer system that may beapplied to any of the computer-implemented methods and other techniquesdescribed herein.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

In general, this disclosure describes flexible sensors for measuring theflex or torque of mechanical structures or mechanical joints. Ingeneral, flexible sensors include a substrate with a slot extending froman edge of the substrate to an inner portion of the substrate, andthereby, forming a flexible arm in the substrate. The sensor includes acapacitive structure formed by edge electrodes located on facing edgesurfaces defined by the slot. The sensor also includes two or moremechanical coupling sites along the length of the slot. When thesubstrate is in an unflexed state, the electrodes are separated by a gapand the capacitance between the two electrodes can be measured. Thecoupling sites are located on the substrate such that when a structureto which the sensor is mechanically coupled flexes or twists theflexible arm of the substrate is displaced by a corresponding distance.For example, a structure to which the sensor is mechanically coupled mayflexe or twists due to a mechanical force (e.g., a load force) or torqueon the structure. In such an instance, the flexible arm of the substrateis displaced by a distance that corresponds with the amount of flex ortwist in the structure that is caused by the mechanical force or torque.The flex in the substrate causes a change in the relative position ofthe edge electrodes with respect to one another, which in turn changesthe capacitance of the capacitive structure. Control circuitry coupledto the sensor can measure the changes in capacitance and correlate suchchanges with a value of flex or torque in the mechanical structure towhich the sensor is coupled.

FIG. 1A shows a top view and a cross-sectional view (at section A-A) ofan example flexible sensor 100. The sensor 100 is constructed from aflexible substrate 102. For example, the substrate 102 can be a plasticsubstrate such as a printed circuit board (PCB). The substrate can bemade of materials including, but not limited to, polymers, elastomers,epoxies and urethanes, or synthetic rubber. The substrate 102 includes aflexible arm 104 and two stationary arms 105. The flexible andstationary arms 104, 105 are formed by two slots 106 in the substrate102. Capacitive structures 108 are located on opposing inner surfaces ofthe slots 106. Additionally, the sensor 100 includes two mechanicalcoupling sites 110 a, 110 b by which the sensor 100 can be secured to amechanical structure or across a mechanical joint. The capacitivestructures 108 are electrically connected to sensor control circuitry(e.g., a sensor controller 124) by wire traces 122.

The slots 106 extend from an outer edge 118 of the substrate 102 to aninner portion 120 of the substrate 102. The length of the slot 106, asreferred to herein, is the distance from the edge 118 of the substrateto the end of the slot at the inner portion 120 of the substrate 102.The width of a slot 106 near the inner portion 120 of the substrate 102is larger than the width of the slot 106 near the outer edge 118 of thesubstrate 102. In some examples, the width of the slot near the outeredge 118 of the substrate 102 is between 0.2-0.3 mm, between 0.1-0.4 mm,or between 0.1-1.0 mm.

The capacitive structures 108 are located at the end of each slot 106near the outer edge 118 of the substrate 102. The capacitive structures108 are each formed by electrodes 112 a, 112 b. The electrodes 112 a,112 b are each located on inner edge surfaces 114 a, 114 b of thesubstrate 102 inside the slot 106. When the substrate is in an unflexedstate (as shown in FIG. 1A), the electrodes 112 a, 112 b and innersurfaces 114 a, 114 b are aligned and face each other. The electrodes112 a, 112 b can be formed, for example, by plating electricallyconductive material along a portion of the respective inner surfaces 114a, 114 b. Suitable electrically conductive materials for forming theelectrodes 112 a, 112 b include, but are not limited to, gold, aluminum,copper, tin, nickel, or a combination of materials.

The electrodes 112 a, 112 b are separated by the distance across theslot 106. Specifically, the electrodes 112 a, 112 b are separated by thewidth across the slot 106 near the outer edge of the substrate 102.Consequently, the capacitive structures have a capacitance, when thesubstrate 102 is in an unflexed state, that is defined by the area ofthe electrodes 112 a, 112 b and the distance between the electrodes 112a, 112 b across the slot 106. Any variation in the position of one ofthe electrodes 112 a, 112 b relative to the other will tend to vary thecapacitance of the capacitive structures 108.

The mechanical coupling sites 110 a, 110 b are arranged on the substrate102 such that mechanical variations in a structure to which the sensor100 is attached will cause the substrate 102 to flex and vary therelative position of electrode 112 a with respect to electrode 112 b. Inthe sensor 100, shown in FIG. 1A the mechanical coupling sites 110 a,110 b are arranged such that one coupling site 110 a is located on theflexible arm 104 near the outer edge 118 of the substrate 102 and asecond coupling site 110 b is spaced from the first coupling site 110 aalong the length of a slot 106. The second coupling site 110 b can belocated near or past end of the slot 106 located at the inner portion120 of the substrate 102.

Referring to FIG. 1B, the sensor 100 is secured to a mechanicalstructure 150 at the coupling sites 110 a, 110 b by using a mechanicalcoupler (e.g., a screw, a rivet, a mechanical adhesive, a weld, a pin,or a clamping device). When the mechanical structure 150 is flexed (asillustrated by dashed lines 152) the end of the flexible arm 104 is alsoflexed (as illustrated by dashed lines 154). The flex in the flexiblearm 104 of the substrate 102 alters the position of the electrodes 112a, 112 b with respect to each other in each of the capacitive structures108, thereby, changing the respective capacitance of each capacitivestructure 108. The sensor controller 124 can detect such changes incapacitance of the capacitive structures 108 and correlate the change toa flex value associated with mechanical structure 150.

In a sensor with two capacitive structures 108, such as sensor 100shown, the capacitance of each capacitive structure 108 may varydifferently. For example, as the distance between the electrodes 112 a,112 b of the upper capacitive structure 108 decreases due to themovement of the flexible arm 104 towards the upper stationary arm 105,the capacitance of the upper capacitive structure 108 will tend toincrease. On the other hand, as the distance between the electrodes 112a, 112 b of the lower capacitive structure 108 increases due to themovement of the flexible arm 104 away from the lower stationary arm 105,the capacitance of the lower capacitive structure 108 will tend todecrease.

In some implementations, the sensor controller 124 can compute adifference between the changes in capacitance of the two capacitivestructures 108 and determine the direction of the flex in the mechanicalstructure 150 based on the sign of the change. For example, a positivedifferential change in capacitance between the upper capacitivestructure 108 and the lower capacitive structure 108 may indicate anupward flex in the mechanical structure 150 (e.g., as shown), where as anegative differential change in capacitance may indicate a downwardflex. The sensor controller 124 correlate the magnitude of thedifferential change to an amount flexure in the mechanical structure 150or a stress (e.g., a bending stress) in the mechanical structure 150.

While sensor 100 includes a single flexible arm 104, in general sensorsmay include more than one flexible arm. For example, a larger sensor canbe constructed that includes three or more slots 106 forming two or moreflexible arms 104. In some examples, the sensor 100 can be constructedwith only one slot 106. For example, a sensor 100 can be formed fromhalf of the sensor 100 shown in FIG. 1A, that includes only one slot 106and one capacitive structure 108.

In some implementations, the sensor 100 can be integrated into a PCBincluding other circuitry not related to the operation of the PCB. Forexample, because the sensor designs illustrated and described herein canbe formed in a PCB any such a sensor 100 can be integrated into any PCBthat is used for control circuity of the mechanical device. Morespecifically, any of the sensors described herein can be integrated intoa PCB that is used for another independent purpose by forming thestructure of one of the sensors at an edge of the PCB. For example,according to some implementations the sensor controller 124 shown inFIG. 1A may represent not only the sensor's control circuitry, but alsoadditional circuitry that is unrelated to the operation of the sensor100.

FIG. 1C shows an isometric view of a second example flexible sensor 175.The sensor 175 represents a variation to the design of that shown inFIGS. 1A and 1B. The flexible sensor 175 includes four mechanicalcoupling sites 110 a, 110 b. Two mechanical coupling sites 110 a arelocated on the flexible arm 104 and two 110 b are spaced apart from eachother and located at the inner portion of the substrate 102. The shapeof the slots 106 of the flexible sensor 175 are modified from that offlexible sensor 100. For example, the shape of slots 106 and thethickness of flexible arms 104 may be modified to accommodate stressesor an amount of flex that a sensor 100 is expected to encounter in aparticular application. That is, slots 106 may be made larger orflexible arms 104 may be made thinner, or both, in a sensor 100 designedto accommodate a larger range of flexual displacement (e.g., +/−100microns) than a sensor 100 designed to accommodate a narrower range offlexual displacement (e.g., +/−10 microns). In addition, the electrodes112 a on the fixed arm 105 (e.g., inner surface 114 a of the slots 106)can extend the entire length of the slot or a substantial portion (e.g.,90% or more) of the length of the slot 106.

With respect to sensor 175 and sensor 100, the flexible arm 104 cangenerally be considered to be the arm(s) 104 that include one or moremechanical coupling sites 110 a located at the end of the arm 104 nearthe outer edge 118 of the substrate 102. The stationary arm(s) 105 cangenerally be considered to be the arm(s) 105 that do not includemechanical coupling sites 110 a located at the end of the arm 105 nearthe outer edge 118 of the substrate 102.

FIG. 2 shows a top view, cross-section view (at section B-B), andisometric view of a third example flex sensor 200. The flex sensor 200represents another variation to the design of that shown in FIGS. 1A and1B. Flex sensor 200 has a generally elliptically shaped substrate 102and includes only one slot 106 and one capacitive structure 108. Themechanical coupling sites 110 a, 110 b are located on opposite sides ofthe slot. In some implementations, the flexible sensor 200 can be usedto measure torque across a mechanical joint coupling two separatemechanical structures. For example, one of the mechanical coupling sites110 a can be coupled to a first mechanical structure and the othermechanical coupling site 110 b can be coupled to a second mechanicalstructure. The joint between the two structures may, for example, extendthrough the slot 106 in the sensor 200.

Any torque force exerted on the joint will flex the substrate 102 andcause one or both of the electrodes 112 a, 112 b to move with respect tothe other. For example, the electrodes 112 a, 112 b may be eithersqueezed or separated as shown by arrows 202 and 204. For example, acounter clockwise torque exerted on the lower coupling site 110 b wouldcause the distance between the two electrodes 112 a, 112 b to decreaseand consequently increase the capacitance of the capacitive structure108. As another example, a clockwise torque exerted on the lowercoupling site 110 b would cause the distance between the two electrodes112 a, 112 b to increase and consequently decrease the capacitance ofthe capacitive structure 108. Thus, in some implementations, the sensorcontroller 124 can determine a direction of torque based on whether thecapacitance increases or decreases and a magnitude of torque based onthe magnitude of the change in the capacitance.

FIG. 3 is a block diagram of an example system 300 for controlling oneor more flexible sensors according to implementations of the presentdisclosure. The system 300 includes one or more flexible sensors (e.g.,sensors 100, 175, and/or 200) communicably coupled to a sensorcontroller 124. As shown in FIGS. 1A and 2, the sensor controller 124may be located on the same PCB one or more of the sensor(s). However, insome implementations, the sensor controller 124 can be remote from oneor more of the sensors. In such implementations, the sensor(s) can becommunicably coupled to the sensor controller 124 by a wired interfaceincluding wires extending between the sensor(s) and the sensorcontroller 124.

The sensor controller 124 includes a sensor driver 302, a capacitancesensing module 304, a flex/torque detection module 306, and, optionally,a communication module 308. The sensor controller 124 can include one ormore processors or microcontrollers. The sensor controller 124 controlsthe operation of each of the sensor driver 302, the capacitance sensingmodule 304, a flex/torque detection module 306, and, optionally, thecommunication module 308.

The sensor driver 302 can be implemented as a hardware or softwaremodule of the sensor controller 124. The sensor driver 302 provides anelectrical driving signal to the capacitive structure(s) on thesensor(s). The driving signal can be an oscillating electrical signal ata given frequency. In some implementations, the sensor driver 302includes a Schmidt trigger coupled to a capacitive structure (e.g., arelaxation oscillator type circuit).

The capacitance sensing module 304 can be implemented as a hardware orsoftware module of the sensor controller 124. The capacitance sensingmodule 304 can detect changes in the capacitance of sensor capacitivestructure(s) based changes in the driving signal caused by capacitancechanges. For example, changes in the capacitance of a capacitivestructure can cause a change in the frequency of a driving signal or achange in the duty cycle (e.g. pulse width modulation) of a drivingsignal. The capacitance sensing module 304 can detect such changes inthe driving signal. For example, the capacitance sensing module 304 caninclude a counter that counts pulses of the driving signal to detectfrequency changes. That is, a change in the number of pulses over agiven period of time would represent a change in the frequency of thedriving signal and a corresponding change in the capacitance of acapacitive structure.

The flex/torque detection module 306 can be implemented as a hardware orsoftware module of the sensor controller 124. In some implementations,the flex/torque detection module can 306 can include a database (e.g., alookup table) calibrated to associate various changes in capacitance ofa capacitive structure to flex or torque values of a mechanicalstructure. In some implementations, the flex/torque detection module 306may not directly associate capacitance to flex/torque values, but canassociated related changes in the driving signal such as changes infrequency or changes in pulse count to corresponding flex/torque valuesof a mechanical structure.

In some implementations, as discussed above, the sensor controller 124can use differential changes in capacitance between multiple capacitivestructures to determine flex/torque of a mechanical structure. In suchimplementations, the flex/torque detection module 306 can include adatabase that is calibrated to correlate data related to differentialchanges in capacitances to magnitudes and directions of flex/torquevalues in a mechanical structure. The data can be actual differences incapacitance or data that represents such differences such asdifferential changes in frequency or pulse counts between drivingsignals supplied to multiple capacitive structures.

In some implementations, environmental conditions, such as humidity andtemperature, may affect the capacitance and, by extension, thedisplacement measurements. The sensor controller 124 can usedifferential changes in capacitance between multiple capacitivestructures, as discussed above, to minimize the effects of suchenvironmental conditions. For example, environmental conditions shouldgenerally effect each capacitive structure on a sensor similarly. Thus,measuring flex sensor displacement distances based on a differencebetween the capacitance of two capacitive structures (e.g., twocapacitive structures on opposite sides of a flexible arm) may reduce orremove the environmental effects on the capacitive structures. In someimplementations, the sensor controller 124 may include facilities tomeasure and compensate for environmental effects such as temperatureand/or humidity on the sensor.

In some implementations, the sensor controller 124 includes acommunication module 308. The communication module 308 can beimplemented as a hardware or software module of the sensor controller124. The communication module 308 can be a wired communication (e.g.,USB) or wireless communication module (e.g., Bluetooth, ZigBee). Thecommunication module 308 can be used to communicate flex/torque data orcapacitance data to other remote computing devices, e.g., a laptop, atablet computer, a control system of a robotic device, a smartphone,etc.

FIG. 4 illustrates an example of flexible sensors 100, 200 coupled to amechanical device 400. The mechanical device 400 can be a robotic devicesuch as a robotic arm. Flexible sensors 100 are attached to variousmechanical linkages 402 of the device 400. The sensors 100 can be usedto measure flex in the linkages 402 that occur during the operation ofthe device 400. The sensor 200 can be used to measure the torque at amechanical joint 404 between linkages 402. The sensors 100 cancommunicate such measurements to a computer control system 406 of thedevice 400. The control system 406 can the measurements to control oralter the operation of the device 400. For example, if the device 400 isused to lift a heavy object 408 that causes excessive stress to one ormore of the linkages 402 as measured by the sensors 100, the controlsystem 406 can control the device 400 to release the object 408, andpossibly prevent damage to the device 400.

In some implementations, the sensors 100, 200 can be integrated into amechanical linkage 402. For example, the linkage 402 can be formed froma material (e.g., a plastic) suitable for a sensor substrate (e.g.,substrate 102 described above). In such implementations, the mechanicallinkage itself can be used as the substrate for sensors 100, 200. Forexample, conductive material can be deposited on appropriate surfaces ofthe linkage 402 to form capacitive structures directly on the linkage402 similar those described above with respect to the sensor substrates.

FIG. 5 is a schematic diagram of a computer system 500. The system 500can be used to carry out the operations described in association withany of the computer-implemented methods described previously, accordingto some implementations. In some implementations, computing systems anddevices and the functional operations described in this specificationcan be implemented in digital electronic circuitry, in tangibly-embodiedcomputer software or firmware, in computer hardware, including thestructures disclosed in this specification (e.g., system 500) and theirstructural equivalents, or in combinations of one or more of them. Thesystem 500 is intended to include various forms of digital computers,such as laptops, desktops, workstations, personal digital assistants,servers, blade servers, mainframes, and other appropriate computers,including vehicles installed on base units or pod units of modularvehicles. The system 500 can also include mobile devices, such aspersonal digital assistants, cellular telephones, smartphones, and othersimilar computing devices. Additionally, the system can include portablestorage media, such as, Universal Serial Bus (USB) flash drives. Forexample, the USB flash drives may store operating systems and otherapplications. The USB flash drives can include input/output components,such as a wireless transmitter or USB connector that may be insertedinto a USB port of another computing device.

The system 500 includes a processor 510, a memory 520, a storage device530, and an input/output device 540. Each of the components 510, 520,530, and 540 are interconnected using a system bus 550. The processor510 is capable of processing instructions for execution within thesystem 500. The processor may be designed using any of a number ofarchitectures. For example, the processor 510 may be a CISC (ComplexInstruction Set Computers) processor, a RISC (Reduced Instruction SetComputer) processor, or a MISC (Minimal Instruction Set Computer)processor.

In one implementation, the processor 510 is a single-threaded processor.In another implementation, the processor 510 is a multi-threadedprocessor. The processor 510 is capable of processing instructionsstored in the memory 520 or on the storage device 530 to displaygraphical information for a user interface on the input/output device540.

The memory 520 stores information within the system 500. In oneimplementation, the memory 520 is a computer-readable medium. In oneimplementation, the memory 520 is a volatile memory unit. In anotherimplementation, the memory 520 is a non-volatile memory unit.

The storage device 530 is capable of providing mass storage for thesystem 500. In one implementation, the storage device 530 is acomputer-readable medium. In various different implementations, thestorage device 530 may be a floppy disk device, a hard disk device, anoptical disk device, or a tape device.

The input/output device 540 provides input/output operations for thesystem 500. In one implementation, the input/output device 540 includesa keyboard and/or pointing device. In another implementation, theinput/output device 540 includes a display unit for displaying graphicaluser interfaces.

The features described can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The apparatus can be implemented in a computerprogram product tangibly embodied in an information carrier, e.g., in amachine-readable storage device for execution by a programmableprocessor; and method steps can be performed by a programmable processorexecuting a program of instructions to perform functions of thedescribed implementations by operating on input data and generatingoutput. The described features can be implemented advantageously in oneor more computer programs that are executable on a programmable systemincluding at least one programmable processor coupled to receive dataand instructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. A computer program is a set of instructions that can be used,directly or indirectly, in a computer to perform a certain activity orbring about a certain result. A computer program can be written in anyform of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors ofany kind of computer. Generally, a processor will receive instructionsand data from a read-only memory or a random access memory or both. Theessential elements of a computer are a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer will also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,ASICs (application-specific integrated circuits).

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what may be claimed, but rather as descriptions offeatures specific to particular implementations of particularinventions. Certain features that are described in this specification inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the followingclaims. In some cases, the actions recited in the claims can beperformed in a different order and still achieve desirable results. Inaddition, the processes depicted in the accompanying figures do notnecessarily require the particular order shown, or sequential order, toachieve desirable results. In certain implementations, multitasking andparallel processing may be advantageous.

What is claimed is:
 1. A sensor comprising: a printed circuit board(PCB) comprising a slot extending from an outer edge of the PCB to aninner portion of the PCB, the slot defining a first inner-slot surfaceand a second inner-slot surface facing, across the slot, the firstinner-slot surface, the first and second inner-slot surfaces beingseparated by a gap when the PCB is in an unflexed state, the slot beingconfigured to permit the PCB to flex so as to vary a relative positionof the first inner-slot surface with respect to the second inner-slotsurface; a capacitive structure on the PCB comprising: a first electrodeon a portion of the first inner-slot surface of the PCB; and a secondelectrode on a portion of the second inner-slot surface of PCB, thesecond electrode aligned with the first electrode across the slot; andmechanical coupling sites arranged on the PCB such that mechanicalvariations in a structure to which the sensor is attached cause the PCBto flex and vary a relative position of the first electrode with respectto the second electrode.
 2. The sensor of claim 1, further comprising acontrol circuit electrically connected to the first electrode and thesecond electrode, the control circuit configured to apply a drive signalto the capacitive structure.
 3. The sensor of claim 1, furthercomprising a control circuit electrically connected to the capacitivestructure and configured to measure variations in a capacitance betweenthe first electrode and the second electrode.
 4. The sensor of claim 3,wherein the control circuit is further configured to determine an amountof mechanical flex in the structure to which the coupling sites of thePCB are attached based on the measured variations in the capacitance ofthe capacitive structure.
 5. The sensor of claim 4, wherein the controlcircuit comprises a microprocessor.
 6. The sensor of claim 4, whereinthe control circuit determines an amount of mechanical flex in thestructure by correlating a measured variation in capacitance of thecapacitive structure to a flexure value among a set of stored values ina lookup table.
 7. The sensor of claim 1, wherein the coupling sites arearranged on opposite sides of the slot.
 8. The sensor of claim 1,wherein the portion of the first inner-slot surface of the PCB and theportion of the second inner-slot surface of the PCB are proximate to theouter edge of the PCB.
 9. The sensor of claim 1, wherein a firstcoupling site is located proximate to the outer edge of the PCB and asecond coupling site is located on a same side of the slot as the firstcoupling site and spaced from the first coupling site along a length ofthe slot.
 10. A robotic device comprising: a member; and a sensorcoupled to the member, the sensor comprising: a printed circuit board(PCB) comprising a slot extending from an outer edge of the PCB to aninner portion of the PCB, the slot defining a first inner-slot surfaceand a second inner-slot surface facing, across the slot, the firstinner-slot surface, the first and second inner-slot surfaces beingseparated by a gap when the PCB is in an unflexed state, the slot beingconfigured to permit the PCB to flex so as to vary a relative positionof the first inner-slot surface with respect to the second inner-slotsurface; a capacitive structure on the PCB comprising: a first electrodeon a portion of the first inner-slot surface of the PCB; and a secondelectrode on a portion of the second inner-slot surface of the PCB, thesecond electrode aligned with the first electrode across the slot; andmechanical coupling sites coupling the sensor to the member, themechanical coupling sites being arranged on the PCB such that mechanicalvariations in the member cause the PCB to flex and vary a relativeposition of the first electrode with respect to the second electrode.11. The device of claim 10, further comprising a control circuitelectrically connected to the first electrode and the second electrode,the control circuit configured to apply a drive signal to the capacitivestructure.
 12. The device of claim 10, further comprising a controlcircuit electrically connected to the capacitive structure andconfigured to measure variations in a capacitance between the firstelectrode and the second electrode.
 13. The device of claim 12, whereinthe control circuit is further configured to determine an amount ofmechanical flex in the member to which the coupling sites of the PCB areattached based on the measured variations in the capacitance of thecapacitive structure.
 14. The device of claim 13, wherein the controlcircuit comprises a microprocessor.
 15. The device of claim 13, whereinthe control circuit determines an amount of mechanical flex in themember by correlating a measured variation in capacitance of thecapacitive structure to a flexure value among a set of stored values ina lookup table.
 16. The device of claim 10, wherein the coupling sitesare arranged on opposite sides of the slot.
 17. The device of claim 10,wherein the portion of the first inner-slot surface of the PCB and theportion of the second inner-slot surface of the PCB are proximate to theouter edge of the PCB.
 18. The device of claim 10, wherein a firstcoupling site is located proximate to the outer edge of the PCB and asecond coupling site is located on a same side of the slot as the firstcoupling site and spaced from the first coupling site along a length ofthe slot.